Justification:
This species has a small population which is thought to be declining rapidly as a result of disturbance at breeding sites, predation and mortality from drift-net fisheries. It is therefore listed as Vulnerable.

Synthliboramphus wumizusume is endemic to the warm current regions near central and southern Japan, where it breeds on uninhabited islands (BirdLife International 2001). The most important breeding sites are in Kyushu, notably the islands of Biro-jima, Koya-shima and Eboshi-jima, and the Izu Islands, notably Onbase-jima and Onohara-jima. Breeding has also been recorded on Gugul Island and Jeju Island off the southern coast of South Korea, is suspected at Dok Island in the East Sea/Sea of Japan (Kim et al. 2012) , and it may also breed in Peter the Great Bay, Primorye, Russia. After breeding, birds move northwards along Japan’s Pacific coast towards Hokkaido, and recent tracking of 3 individuals found that 2 birds travelled along the coasts of the Japanese archipelago in an anticlockwise direction during the course of a year, whereas the third bird moved up and down the Pacific coasts of Japan’s main islands (Yamaguchi et al. 2016). Early winter movements include southwestward along the coast of Primorskii, the People’s Democratic Republic of Korea, and the Republic of Korea or southwestward along the Pacific Coast of Honshu and Shikoku. Birds have been found to winter in the southwestern part of the Sea of Japan, or move southward into the Pacific Ocean (Yamaguchi et al. 2016), with some apparently moving south to the Nansei Shoto Islands. The population is unlikely to exceed 10,000 mature individuals. It is still declining in many localities, particularly the Izu Islands (Carter et al. 2002).

By 2015, 38 colonies (current and historical) were reported, with a total estimated population of 2,600-4,700 pairs (Otsuki and Nakamura 2016), equating to around 3,500-10,000 individuals. National population sizes have been estimated at < c.100 breeding pairs and c.50-1,000 individuals on migration in Korea and c.100-10,000 breeding pairs and c.50-1,000 wintering individuals in Japan (Brazil 2009).

Trend Justification: Populations are thought to be declining rapidly through the combined impact of predation by introduced rats, disturbance of breeding sites and adult mortality in fishing nets.

It frequents rocky islets and headlands during the breeding season (between mid-February and early May), nesting in single pairs, small groups and sometimes in large colonies. In the non-breeding season it occurs offshore, occasionally entering bays. Juveniles have been sighted outside the breeding season in the Seto Inland Sea, an area previously thought unsuitable for Japanese Murrelet, at least 150 km from the nearest known breeding site (Iida 2008). This was confirmed by the sighting of several family parties around the south-west of Yashima Island in the western Seto Inland Sea (Iida 2010). Two adult and two chicks with down, seen close to the coast of Tateyama City at the south end of Boso peninsula, point to other unknown breeding locations, as these sightings were 70 km from the nearest known breeding islands (Fujita 2008). Breeding is suspected on Dok Island in the East Sea (Sea of Japan) from a dead chick recorded on Seo Island in 2005 and an adult with two fledglings filmed in 2009. More recent records confirm a further breeding location in southern South Korea based of a downy chick photographed on the south coast of Jeju Island, and one adult and two juveniles seen and photographed at sea between Gapa and Mara Islands offshore from Jeju Island (Kim et al. 2012).

Sport fishing on isolated offshore reefs and islets is a major threat as it causes direct disturbance and habitat degradation. Fish, discarded by anglers, attract crows and gulls which then predate eggs and chicks. Indeed, predation by crows is the main threat on Biro-jima and Onohara-jima. Brown rat Rattus norvegicus has been introduced to some nesting colonies and has almost extirpated the population on Koya-jima, after rats had been successfully eradicted in 1987/1988 until 2006 when they were reintroduced, and then possibly eradicated for a second time. Landings by fishermen pose a continuing threat of rat reintroduction (M. Sato in litt. undated). Annual mortality of adults in drift-nets has been estimated at 1-10% of the total breeding population, but these figures may be underestimates. There is some evidence that fish stocks have declined around the Izu Islands because of changes in water temperature. Oil spills are a potential threat.

CMS Appendix I. It is legally protected in Japan. In addition to the several breeding colonies already protected as national wildlife protection areas, including Nanatsu-jima, Kiinagashima, Okino-jima and Danjo-gunto, in November 2010 Biro-jima, Tadanae Island, Ohnohara-jima and Kanmuri-jima also received this designation (K. Ono in litt. 2012). Gugul Islet (South Korea) has been designated as a Natural Monument. In Japan, educational materials have been produced to inform fishers about the species and the importance of the largest known breeding colony on Biro-jima Island, and research on nest predation is ongoing.

Conservation Actions Proposed

Conduct coordinated surveys of breeding sites to determine current population size and trends. Establish new protected areas at important colonies that are not officially protected. Restrict human access to islands with breeding colonies. Control predators at breeding colonies and establish artificial nest boxes. Research and design methods to reduce the bycatch of seabirds by fisheries. Improve understanding of non-breeding movements and threats.